5) Question 5 (5 pt) You are characterizing the firing rate of a neuron by conti

Question

5) Question 5 (5 pt) You are characterizing the firing rate of a neuron by continuously injecting different amounts of current into the cell. You plot the results:

a. (1 pt) From this data, what would you conclude is the duration of the absolute refractory period of the neuron? Briefly explain your thinking.

b. (2 pts) Briefly explain (1-2 sentence) the difference in the mechanisms underlying these two types of refractory periods.

c. (2 pts) The neuron you characterized above is a pain-sensing neuron (“nociceptor”) from a person with a disorder that makes them hyper-sensitive to pain. You believe the condition is caused by the neuron firing at a higher than normal rate when stimulated. Come up with an idea for a drug that would act on a voltage gated ion channel to help this person. Remember: we want to keep the person’s ability to feel pain, but we want to reduce the pain they feel. For that reason, the drug should reduce, not eliminate, the firing rate. Explain how your drug would work and describe (or insert a sketch of) how the shape of the action potential would change after adding the drug. Firing Rate vs. Simulating Current 550 500 450 400 1 N 350 E 300 ? 250 150 100 50 350 100 150 200 250 Injected Current (pA)

Explanation / Answer

A) Refractory period is the phase immediately following the action potential where the nerve/muscle is inert to further stimulus. Refractory period contains two phases: absolute and refractory. The duration of absolute refractory period ranges from 1-2 milliseconds.

B) Absolute refractory period is the phase during which the nerve cell cannot be re-excited however large the intensity of stimulus may be. In relative refractory period, the nerve can be excited if the strength of the stimulus is high.

C) Perception of higher intensity of pain could be due to nerves having minimal refractory period. The drug that prolongs the refractory period of neuron may decrease the frequency of firing of nerve cells and therefore nociception decreases.

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